Coldplay Wristband
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A friend recently saw Coldplay in Glasgow and returned with stories of synchronised flashing wristbands. Of course, I was naturally intrigued. Sadly since the gig, she was unable to make the wristband turn on the LEDs so I offered to have a look inside.
From watching various youtube videos (www.youtube.com/watch?v=wfv7vpc-c1U) they seem to have a way of wirelessly controlling different groups of wristbands. At a guess that's linked to the CODE printed on the housing (in this case: XYLOD6pk).
Opening up the units shows some very compact circuitry including an Atmel MEGA48PA (a versatile low-power 8-bit microcontroller).
Power is provided by 1x CR2032 3V coin cell on the top, and 2x CR2016 3V stacked coin cells on the base. So you certainly shouldn't just thrown the wristbands in the bin, the batteries should be disposed of in your recycling bin instead (check your local council for details). The electronics should also be dealt with under the WEEE Directive.
The part I was most curious about is how they received the radio commands to switch on/off the LEDs. Given that there is sufficient control to uniquely identify groups of wristbands then we're looking at some form of RF protocol, perhaps a WPAN multi-hop mesh? Or just a simple multi-hop flooding protocol would probably work. There was no immediately obvious antenna (although it would make sense to utilise the power strips to the LEDs around the wrist). There's a U2 chip hidden by a small mound of potting that is most likely the RF transceiver connected to a 10MHz crystal X2. You could possibly manage it with a IEEE 802.15.4 transceiver.
Markings on the PCB are VER:02 HPRB01.
Hopefully these wristbands will be utilised at future gigs; you can't go far wrong with synchronised flashing LEDS :)
Anyway, I haven't yet figured how to let my friend switch her LED wristband on with the radio comms. Maybe they'll release a USB dongle so you can have synchronised flashing with your home stereo/MP3 player? :)